[clang] [clang-repl] Implement LoadDynamicLibrary for clang-repl wasm use cases (PR #133037)

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llvmbot wrote:

<!--IGNORE-->
>The above failure reported doesn't look related. Cherry picking commit for 20.1.3
>
>/cherry-pick [8f56394](https://github.com/llvm/llvm-project/commit/8f56394487a4d454be0637667267ad37bd636d0f)

Error: Command failed due to missing milestone.

https://github.com/llvm/llvm-project/pull/133037